Professional Engineer Norman Becker solves readers' dilemmas ranging from tree-root patio bulge to bracing a floor joist under a toilet.

Q: We have a patio covered with modular concrete pavers that are being pushed up by a river birch that we planted nearby. The birch is about 12 in. in diameter and is about 6 to 7 ft. from the patio. Can we remove the part of the root that's pushing up the pavers? And how do we then repair the patio?

ERIC WICHERSKI

LINCOLN, NE

A: Cut a tree root and you risk killing, or at least seriously harming, the tree. Removing one large root may eliminate 25 percent of the tree's total root system, according to Jim Skiera, executive director of the International Society of Arboriculture (ISA). But, if you're careful you should be able to reduce the risk significantly.

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Make your cut as far from the trunk as possible, says Skiera. To see how close you can go, measure the diameter of the trunk, in inches, at a point 4-1/2 ft. above the ground. Then multiply that number by 6. The resulting figure reflects the minimum distance that you need to keep away from the trunk. In your case, Skiera's formula indicates that you should cut the root at least 72 in., or 6 ft., from the tree's trunk. (For more information on tree care, take a look at the ISA's tree-care Web site: www.treesaregood.org.)

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Having determined where you can safely cut the root, you are ready to take on the task at hand. The patio pavers will need to be reset at the end of the process--which makes it fortunate that you have a modular paving system, rather than a monolithic one. You will have to pry up the pavers, set them aside, cut through the root using a bow saw, then replace the pavers' substrate. Either use a hand tamper or rent a vibrating plate compactor to pack down the substrate material firmly. When you're finished, you can lay the pavers back in place.

Unfortunately, Skiera says, the patio probably will need attention again in a few years. Severed roots react by producing large numbers of smaller roots. This compensating growth likely will need to be cut back repeatedly.

5 NEW/OLD TOOLS

The square, line, knife, ruler, screwdriver and saw are some of the oldest tools known. The line is so ancient you can find a biblical reference to it (King James Bible, Job 38:5). So long as people use tools, designers will come up with new ideas for making them better--as the five products here demonstrate.--Roy Berendsohn

1. GEAR-DRIVE CHALKLINE

Why: Irwin's chalkline has a gear drive with the fastest retrieval we have seen. Its free-spool feature helps you pay out line rapidly without making the crank turn. Cost: $11 with 4 ounces of chalk powder. Contact: www.irwintools.com

2. INSULATION KNIFE

Why: This C.H. Hanson knife has a smart innovation to show off: The wheel pushes the insulation down ahead of the blade, making cutting easier. Snap off sections of blade to expose a sharp edge. Cost: $15 at home centers and hardware stores. Contact: www.chhanson.com

3. SAW/SCREWDRIVER

Why: Driving screws and sawing wood, metal or drywall are all quickly accomplished with the General Tools Quad Saw/Driver. Its pivoting handle has a collar that locks on a 1/4-in. hex-bit holder. Eight screwdriver bits come with the tool (shown below left), plus three saw blades and a holster. Cost: $20 at home centers. Contact: www.generaltools.com

4. OFFSET SQUARE

Why: One advantage of the Modified Square's offset design is that it reaches around projections like a table edge. The offset also forms a handle to help you reach more easily into a corner than the traditional 90° steel square. Cost: $25 plus $5.75 shipping. Contact: www.modifiedsquare.com

5. DIGITAL TAPE MEASURE

Why: Starrett's 3-volt, 16-ft. Digitape has a conventional tape, but also reads digitally in English and metric units, with whole numbers and fractions of an inch or in decimal units (0.3 ft., for example). Choose your readout with the press of a button. Cost: $50. Contact: www.starrett.com

There's nothing like drywall repair to get the creative juices flowing. We're still fielding letters about our article on the topic in February 2005 (page 85). Here are reader tips ... and one from me.--R.B.

Cut a square piece of drywall to cover the hole, then on the back of the patch remove a thin strip of drywall along each edge without removing the paper. Done correctly, this forms a paper flange on the patch's perimeter. Apply compound to the paper and press the patch in place. There is no tape, no backing board, no screws, no finding studs.

--Bob Martin, Philadelphia

Install a hinge-pin doorstop or a baseboard stop to prevent future doorknob damage. And use an 8-in.-wide drywall knife, as opposed to a 6-in., for a smoother repair.

--Jimmy Theriot, Shreveport, LA

My favorite fix for small to medium holes is to cut an accurately shaped patch that is about 1/8 in. smaller all around. Drive a drywall screw through the patch's front, then butter the edges of the patch with drywall compound--much like you would apply mortar to a brick. Using the screw as a handle, push the patch into the hole and let the compound dry. Remove the screw, sand the patch smooth and apply a layer of compound. Tape it if necessary.

Flickering Fluorescent Bulbs

Q: The spiral compact fluorescent bulbs in my shed flicker when I turn them off. The light switch is not a toggle type but is a pushbutton timer. Is the switch the problem?

PAUL GOODE

VIA E-MAIL

A: Modern electronic switches use semiconductor devices such as a triac to control a lamp circuit. The distortion created by these devices produces unwanted currents and voltages in the circuitry of a compact fluorescent lamp (CFL). The result is that the bulb will flicker and its life will be reduced, according to Gary Crawford, CFL product manager for General Electric's Consumer & Industrial division. That's why manufacturers don't recommend CFLs be used on circuits controlled by timers or photocells. Either replace the switch with a standard toggle type or change to incandescent bulbs.

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A typical guy's summer projects might range from laying out a patio to marking out a baseball diamond to installing a new fence. These jobs have one thing in common: the need for precise 90° angles. The best way to get those angles is with batter boards and the classic 3-4-5 triangle. Batter boards are a simple lumber assembly used to support layout strings. You take the two strings--which can be as long as you need--and make them perpendicular to each other using the proportions you learned back in geometry class. Starting at the point where the strings cross, mark off a 3-ft. section of one string and a 4-ft. section of the other. These are the legs of the triangle. Then use a tape measure to make sure the hypotenuse is 5 ft. long. The result is a 90° angle. A nice benefit is that it's easy to duplicate on a large scale. A 9-12-15 (ft.) triangle is a supersize version of the 3-4-5.--R.B.

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Noisy Plumbing

Q: I hear a bumping noise a few minutes after I finish taking a shower. It's not loud, but it is annoying. The noise happens only when the hot water is used. Is this a problem that I should fix or something not to worry about?

JAMES WAGGONER

ATHENS, TX

A:The fact that you hear the noise only when hot water is used in the shower is a clue to the source of the problem. Copper pipes expand when hot water flows through them. It's likely that the noise you hear later is the hot-water pipe rubbing against a stud, joist or support bracket as it contracts.

In all but the most severe cases, the condition will not cause a leak. And it can be so hard to correct that unless you are already remodeling, the work is not warranted. You would need to remove the drywall everywhere you hear the noise, and insert a piece of foam rubber (or foam insulation) between the pipe and the framing.

Working in construction, I get to build some great structures for other people. I decided to build this lighthouse/waterski shack as part of a project to improve my home. It reminds me of growing up in Michigan and boating on the Great Lakes. The lighthouse is on Lake Dunlap, near my home in south-central Texas. About 80 percent of the material is salvaged, some of it from an 1890 farmhouse. The front door is from a Navy ship, and took me four months to find. I used 2 x 6 wood studs and skip sheathing on the outside, and finished the exterior with Alaskan cypress tree shingles--they're maintenance-free and should age nicely.

The hardest part was to design each phase before I ever picked up a board. I drew, and re-drew, everything to scale until I got the design proportionally and aesthetically correct: 20 ft. tall with an 11-ft. base. When the design was complete, I built it as separate components and hoisted these into position. Inside, there are no ceiling joists, just a spider web of wooden beams, so you can see all the way up to the bottom of the roof. The wooden interior has built-ins for storage, a refrigerator, a marble countertop that extends through the wall to the outside, and a stereo/DVD system that is great when we have parties.

The whole project took about two years. The only problem is that when I come outside in the morning and see the lighthouse and the water, I feel so comfortable I don't want to leave.

GARY VERLINDEN

NEW BRAUNFELS, TX

FOR YOUR PROJECT TO BE CONSIDERED, please send clear, color photos and a brief description to: Reader Project, Popular Mechanics, 810 Seventh Ave., 6th Floor, New York, NY 10019, or e-mail your project to popularmechanics@hearst.com. Any letters and pictures submitted become the property of Popular Mechanics. Unfortunately, we cannot return submissions.

Mind On The Gutter

Q: We recently had a new roof put on our house. Now, every time it rains, water runs between the gutters and the house. We would like to correct the problem by installing gutter aprons, but lumberyards in our area don't seem to stock them.

JAN ADAMEC

WOODSTOCK VALLEY, CT

A:The problem is probably one of semantics. The "gutter apron" is better known by another name, "drip edge." The drip edge is placed under the bottom row of shingles to prevent water from running down the fascia board and getting behind the gutter. After receiving your letter I called a local lumberyard that sells roofing supplies and asked if it carries gutter aprons. The clerk's answer was, "What's a gutter apron?" I then asked about drip edges. Sure enough, his response was just the opposite. As it turned out, the lumberyard had copper, aluminum and galvanized steel drip edges. And, the clerk was only too eager to inform me that they came in 10-ft. lengths and in several colors. I suggest you try your local lumberyards again.

Concrete Floors and Moisture spans 153 pages, nine chapters and an appendix, giving the essentials of what concrete is, how it cures, and the wide variety of things that go wrong with concrete floors that were built improperly--some of them before modern standards were established. And a lot can go wrong. Mold, peeling floor coatings, popping tiles, lumps and cracks in the flooring above or in the concrete itself are among the problems described. The remedies are not easy, the book makes clear. They range from tearing out the floor to managing a problem with ongoing repairs. Especially important to those building a new home is Chapter 8, "Architectural Details for Floor Construction." This chapter shows you how to build a well-insulated, moisture-resistant floor. The book costs $40 plus $8 shipping. Contact the Portland Cement Association at 847-966-6200 or go to www.cement.org.--R.B.

Boring Holes In Rock

Q: I need to bore a number of 1-1/2-in.-dia. holes 1/2 in. deep in rock for some craftwork I have planned. Can you give me any leads on the tools I need and where to buy them?

TIM WITTMAN

ANACORTES, WA

A:To drill into stone you need a rotary hammer and a diamond-tipped bit. If you can't find a diamond-tipped bit, try one with a carbide tip. These tools can be purchased at home centers and are available on the Internet, as well. Here are three Web sites where you can find what you need: www.mytoolstore.com, www.amazon.com and www.boschreconditioned.com.

Bracing A Floor Joist

Q: We recently had our large bathroom remodeled into two smaller bathrooms. During construction, a new toilet was positioned above a floor joist, which had to be cut to allow the drain to run through. The contractor says the joist does not have to be braced since the subfloor above it is 3/4-in. plywood. Is this correct?

JOHN C. COLWELL

SAN DIEGO, CA

A:Additional bracing is needed. Floor joists support the surface above--not the other way around. The concern here is not that the floor will collapse. The subfloor will provide enough support to prevent that. However, the unsupported section of floor will deflect more than if it were properly supported. This can cause nearby tiles, and the joints between them, to crack.

We asked Mike Casey, former president of the American Society of Home Inspectors and coauthor of Code Check ($17.95; Taunton Press), to suggest a remedy. "Use a header of the same thickness as the floor joist itself and attach it at each point where the joist was cut," he said. "This will distribute the load to the adjacent joists."

In most cases, that's all you need to do, but you also should check with your local code enforcement office to see if there are specific requirements that go beyond national building codes. For example, said Casey, "you can use joist hangers to attach the header because it makes the header easier to install, but hangers are not required unless the header spans at least 6 ft."

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